trbojevich



sept. 22, 192s.

. l Re, l"16,172 N. TRBoJl-:vxcH

HOB

y original Filed Ja.- 5, l1922 3 Sheets-Sheet 2 sept.22,1925. y Re,16,172 N. TRBOJEVICH HOB origina Fileld Jan. s. 1922 s sheets-sheet 2 sept. 22, 192s. Re, 16,172

N. TRBOJEVICH HOB ,original Fileduan. 5. 1922 3 sheets-sheet s residing'at Reissued Sept.` 22, 1925. v

UNITED s 'lATEZs PATENT. oFFlcE. l

NIKOLA'TRBJEVICH, or HieHLAND PARK, MICHIGAN, AssIGNoB. To GLEAsoN womis,

j or RocnEs'rER, maw- YOBK, A conroRATioN or NEW Yonx.

originar No; 1,465,151, eared To all whom t may concern:

Be it known that` I, NIKOLA formerlya subject of the- -King of'Yugoslavia, but now a` citizen of the UnitedStates', i Highland Park, in the county of lVayne and lState of Bichigan, have invent ed certain new and useful'lmprovements in v` .HobS, of which the following is a specificacompanymg drawings.

fthe .speciicationand the appended claims.

Thel hob Which'iorms the subject of this` fy Inf theA present state i Vgears where the teeth and interdental spaces tion, reference -being had therein to the ac- This invention relates to hobs and One object-of theinvention is the provi-v sion cfa lliob, capable of producing symmetrical teeth on gear blanks, 'which' will be easy to construct and which may be readily main-4 tained in operativecondition. j

-Affurther obj ect is the provision' of hob w'hich'will produce teeth upon conical gear blanks without mutilation or interference.'

" Other'obj ects will appear hereinafter'from invention has" been found to be especially useful in the lproduction vof bevel gears, or. gears produced from conical blanks,` and is in connection with such gears that I shall describe its structure.

of theart hobbingfis extensively used inthe manufacture of spur 'are of uniform cross-section, but the methods y employed are vnot :applicable inthe .generation; of'teetlr on conical blanks. C The di ili. culties encounterednare first, the changing `-pitch and changing tooth cross-section of the y .conventional vstraight tooth ;bevel gears` .which renderjit impossible to produce such gears by anv ordinary hob, and second, with bevel gears having spiral or curved tee'cl1,'orI

. any gears produced from conical blanks and provided with longitudinally curyed teeth, one surface is concaveAv andof a curvature' which would preclude the use of the ordi-4 nary cylindrical hob 'without linterference.

" It-'hasbeen `proposed to use 'a conical hob,

but' these have required a helicalv thread of varying'lead and the dilliculties of manufacpractical'. Furthermore, even` if suchhobs ture and maintenance of hobs are too great to render Vtheir 'use for thispurpose ould 'be vmadefthe gears generated thereby Taoanvioigg.

discovered more'over,that this hob may-.be

riapre particularly, to. hobs for producing gea-rs.

' in dotted lines;

, would be' defective. With thehdb which' "1 forms thesubj ect offjtihis invention, however,

August 14, 1923, serialv $0,526,512, med January 3,1922. Application far reissue filed March 14, 1925. Serial No. 15,665.

I have found itentirely possible to produce proper teeth `upon conical blanks. I have used in the manufacture of a novel typeof4 gear, wliichis also myinvention and which is claimed ina separate application; For the purpose of clearly describin the.

structure of the hob which orms'the su ject l ot this invention,- reference may 'behad lto the accompanying drawings, in which I have illustrated one embodiment of the invention,

it being understood, however, that m invention is not limited to the specific em odi'- 'mentpshowng but. is capable of-inodii'cation.V Vwithin' the scope of the invention and vlilnlts of the appended claims.

ln the drawings: Figures l to 4 show geometrical principles involved;

diagrammatically the Figure 5 is a' sectional .elevationof the hob'A indicating a gear blank being operated upon,

a double threaded-'hob of the( preferred fol.m; Figure is' asimilar `view of a modified construction. f

Figure 8 is a diagrammaticview showing a section 'through the hobl thread, taken'in a plane tangent toits pitch surface, and showing various positions of the thread in cutting Figure 6 is fthe pitch cone development of v To understand he improved-construction y of my hob, I have described it in connection with a novel form of gear which may be produced by :this -hob' and in 'connection with' the geometrical principles involved. in i theproductionrof this novel form of .gear. 7 as shown 1n Figure l, ais a pointfon a line orastring b which is vbeing unwound' from a base circle-.en ,drum c :and which circle. A Series Aof equi-spaced points I(t, a', vetc., will g'fs'en'eratefl similar curves, all o'f which are parallel Vto each other. l If' the tracing points, instead oit beingVdire-ctlyin the line b, are in a vline ef'ofset therefrom but parallel thereto and rigid therewith, as i* shown :at f, f etc., in'Figure 2, such points will generate curveswhich are nonfparallel" and outwardly .divergent 'and may be designated as extended modified involute curves. Ifv thev oiiz'setting-of the line is inward'from ,the base circle',"as shown atg in. Figure '3,

'95 Atraces a curve thatfis an involute oa and thenthe vequi-spaced points 71 z. etc.,

termed abridged modified involute curves.

If the inward offsetting of the line is equal tothe radius of the base circle, as shown in 'Figure 4, the curves traced by the equis aced oints etc-'are true Archimedean P P @a a a spirals; that is,'there isa constant ratio between the 'vectorial angle and the radius vector. f

It willbe seentthat-the curves of the three above 'named series are non-parallel tapering hob A mesh-ing with a 4spiral gear `G of thejimproved construction," showing v whic :and areoutwardly'divergent, 'It is known from geometry 'that finv'olutes .only (not' p, fcur'ves varev equal y necessarily of a circle) 'form series of parallel curves. In that case the' 'generat-- ing line is al common normal to Ievery curve of the series. However, theiirst named curves are not `common involutesbecause the generating lineV at every instant rotates about an offset point and, therefore, is not y a normal to any' curve of the series. Thus,

the curves are non-parallel and the distance 4'between two consecutive: curves is always less 4thanthesfpa'cing yf', f f 2,etc., of the generat` ing line fe Figure 2.- They are also'outwardlydiv'ergent beca-use .they approach a series of parallel -involutes asymptotically .and the normal pitch (the shortest distance.

between two consecutive curves) ``also `asymptotically approaches its-i maximumval my invention, showing 'in side elevation `a that `the axial section of the hob forms [a rack ofconstant pitch and engages the gear alon a geodesic-line that-is 'a conical helix Voiiset straight line e of Figure 2; Thehob is, therefore,^of rack section along a genera= 'the curves of which. are. Archiinedean4 spirals. -If'any radial line j'be taken andv normals are drawn' from the several curves -at the points of intersectionwith .the line j,-.

as indicated at 1, k., etc-,these normal lines will all extend' to -af common pointl -which point may be defined as the 'end ofthe polar subnormal belonging to the'fveetor l points of intersection of the thread with the radial line is di'erent at each' poiiito inter` b e true forany radial line .j and for :any h ne corggwhichjis'otl'set from the base clrcle a distance :equal. to the'other polar',

:between thepithllrfaoes ffitliehbb and v crovvngeanf n Figure '5 represents a preferred Iform ofstated, it is evidentr'that.,

angle. Thepoint] lieson the -base circle c .of the hob and is on aline perpendicular to the axis of the hob. "Nuruerically, the length vof the polar subnormal equals vthe lead-of the spiral. (i'n'development) divided 70 by 27:, andis always ymeasured perpendicular to the radius vectoi'.'- Also, if the Vspacing of the curves in Figure 6-correspondsto the spacing of the-points@ i', ete.,Figure 4,

I'the'one figure, maybersupe'rimposed upon'75 the other and both-the curves andv normal' lines will' coincide, Again, if the distance of 'the' polar .sub-normal from the radial .center o fi Figure 6 is equal to the` offsetting ofthe lines e 'or Figures 2 and 3, and the 80 spaced along saidlines,

then Figure '6 maybe placed on either; ofthe tangent vto each" oth'e'n lThis relation will C sub-normalf.'v Figures' 2 and 3 are. diagram?.A maticd'evelopmentscf the novelkform' of gear which maybe reduced with my hob,` 9W ofthe crown' gear 'c a ,system ofintcrmcsh-j 111g .gears of this novel. form The. hdl?,

From fthe' geometrical whichi's of'constant Ieadandl fore- Pin 'development-*isf fan?.4 spiral may.be'- used "for generating 'gear teeth` of either ythe extended for* abridged inter ference v'or`:mutilation of ,one y-portionof the gear and the generation of .another .-portion.

It 1s, however, essential fr ythe production -of theoretically-correct gears vofthis' typey that =`the'.distance betweenthe axisy of the 110,-' in Figure '5f taken in the' pitch cone, Aall of respond -L hob 'andzits'ipolar sub-normal should cor- 1n jdesigni-ngg'thehobthe dimensions are se-v '.lected; with this viewf, 'essary irx' tlie producti`on of such 'gears lthat ShU.'

leurvature'of "the helicoidal face of the hob "51120 medean spirals because those spiralsY are they A i `'only curves for which the length 'of the .j polar subnormal is the "same-:for all fointsI` of the curve. lThe thread oftheh will7 n intersect this radial line' fj at. increasingly acute angles, andl since the angle formed lthe norma-ls'and the radialline j at" the" 'It is further nec- 115 belsl'i'h 1 that 'thejmormah radius of i hob is, -the re fore,-made preferably concave on the side'faci'ng'the apex and convexl on the other. ;Tl1e newl hob-"will, as" shown particularlyIiuFigure 8, correctly lproduce curved teeth on-"conicallblanks without mutilation,` .130

hence,'i's capableofme'shing with .the crowni gear, orthe;

y position a toposition b.;

i blank G, the hob 'sweeping out a tooth `in. its movement, relative to the blank', from lfigure rshows the Yhob-in `its action on a gear space As "specically .shown in .Figure 6,1 the i thread m of the hob is a double thread, but

this isnotessential as the hob will operate with either'" a single thread or ainultiple thread.

I'The cuttingcdges are formed byrlongitudinally gashlng the thread, asindicated ata, the number ofthese gashes determin? A ,I ing thejnumber'of separate cuts that are takeninreachrevolution of the hob.

offa certainfhob only the well known mathematical` rules need to 'be' followed. 3, The

cone angle'and the lead of thread in -a hob (measured alon the side and notyalongv the axis of the hog) thedeveloped lead to the lead of the ,hob divided by the sine' arel known. Fromfthat may be-obtained as equal of the'cone angle. By further dividing ysaid u quantity by 2r, the exact value ofthe polar A subnormal is obtained.

It' is desirable thatthe modification ot the I tooth curves (preferably vextended invoi figures.

lutes) be exactly the same as the said polar subnormal. Hoyvever,l for practical pur- Such.. a departure may bev advisf able when the hob is larger in diameter than would be ltheoretically required.v In such' a case al slight decreaSeOthe modificationl of the tooth curves serves to compensate -for the oversize hob.

A. ity in construction, its developments an Archlmedean spiral, 1t

VVhileI prefer, oniaccount of simplicto -use a hob which in is possible toform a hob-of other .curves of production of curved toothbevel gears, so as 5 to be equal in extension or abridgrnent'to the `cur-ve to be generated thereby.

In'Figure 7 the'pitch-cone'developmentot a hobof general involute character' is shown.

extended involutes developed 'from the base thread linesjm, m, etc., and'may be either edges, as will be understood. Such hobs are .sharpened by grinding the faces of the poses, there is considerable latitude permitgears ymay be obtained departing fromthe theoreticalv the modified involute type, it being only es- .sential to select said curve, when used in the The cutting teeth 19,19*', p2 are"arranged on the face of a truncated co'ne body'in a series of thread lines m,m, etc., which forrn'similar A straight orv curved. The remaining portionsV of the .thread are relieved to form cutting flutes, 'similarly'to the processmemplpyed for. sharpening of the ordinary hobs. AWhile I have described my invention in connection with the/.production of a particu'lar` type of gea'r it'is to be understood that the structure or use of the hob may be -modified or variedv Without departing from the intention .of the invention or the scQpe'of the followin claims, and that this application is inten ed to cover any adaptations'or.

embodiments, `following, in general, 4the principles of the invention and includingsuch departures from 'thel present disclosure-'. as come within knownor customary vpractice Inggear cutting and may be applied top the essential 4features hereinbefore set described my invention,

*helix which in development and in comparison with the developmentof the gear generated thereby has longitudinal tooth curves traced by points equispaced from lines rolling on the base circles respectively of the hob and gear.

" 2. A hob or cutter -for generating spiral vbevel gears comprising ay tapering helix which-.in development isan Archimedean spiral havinga polar sub-normal selected to'correspond with the modification of the longitudinal tooth'curves of the gear from involutes'of a circle.

A hob or cutter for the generation of spiral bevel gears comprising a tapering hel-ix` which ingeodesic section forms. a rack ofconstant pitch and which in development orms'a series of longitudinal tooth curves ,of modiied involuteform and having a predetermined. relation to the longitudinal tooth curves of the gear generated thereby. 4. A hob or'cutter for the generation of spiral bevel'gears comprising a truncated tapering. helix vwhich in axial section forms a rack of constant pitch and which in developmentforms an Archimedean spiral having-a polensub-normal selected with respectto a predetermined longitudinal tooth curve of modified involute form in the gear to be generated;v

5. A hob or cutter for; Spiral bevel gears lcomprising a truncated tapering helix longitudinallyga'shed to'form cutting edges, said helix forming in the axial section ot the hob a racket constant-pitch and in development forming`-Archimedean spiral curves having a polar subfnormal'selected with reference tof predetermined longitudinal tooth curves 'ofmodified involute form in thegear to be generated.

Q6'. -A hob or cutter- ;for the generation of 'spiral bevel gearscomprising a bodyhaving :atapering-helical-threadwhich in axial sec.-

forth and as fall within the limits of the In computation of theA polar subnormal" Y .dition fornis-i a. rack'of. constant pitch and f type.

whichA in development forms non-parallel modifiedinvolute curves, said" curves being generated by a rack of constant pitch spaced from and parallel to aline rolling on abase circle of predetermined radius. l

'7. A hob or cutter comprising a tapering helix longitudinally gashed to form cutting edges, said helix forming in geodesic section a rack of Constant pitch and in development formingT a spiral of the :general involute 8. A hob or cutter comprising a body having a tapering helical threadlongitudinally .'gashed and transversely relieved to 4 form cutting edgesy's'aid thread being capable .of meshing with a rack element of constant pitch along a series of geodesic lines and forming in development a. spiral of the general involute type.

9. A hob or cutter comprising a frusto` lconical body A. provided with a tapering helical thread,\ vhic h, indevelopment, forms of rack section along a' 4aj-spiral of the general involute type, said thread'being capable of meshing with a rack i element of constant pitch along a series of geodesic lines and being longitudinally gashed and transversely relieved to form cutting edges.

10. A- hob formed by gashing a thread- Which presents a series of curves in de velop',`

ment which are of constant lead. y

.11. A taperhob 'formed by' gashing a thread'which presents a series ofI curves-in development which are of -constant lead and generatrix of the pitch surface of the hob., 12.A: hobj formed by gashing'a thread one Side of'which in a section lthrough the thread 1in a plane tangent to the pitch surface', thereonfisconcave. -v 13;:A taper *hob formed by gaslnng thread having a pressure angle, .on the side .facing the apexof the hob, -less than the pitch cone'anglefof. the hob.

14. AQta'perhob,y formed by gashing a l thread-which in section in :a .plane tangent pitch 'surface is of general crescent shape. y y

15. A` taper hob `l formed j by gashng a thread having a pressure anglefon the side facing theapexof the hob less than the pitch .cone ang-1e ofthe hob and havingapressureangle on the opposite side greater Vthan the pitch cone angle of the hob.

16., -A hob orm'ed'b'v gashing a thread' the `perpendiculars to which at the pitch' surface along a straight line. in development meet .in-a single point. A i

lying on thev base circle of the hob.I

'- of the general involutetyp'e.

17. A taper hob formed by gashing a thread the perpendiculars to Which at the pitch surface along a radial line in developnient meet in a single point.

18. A hob fornied by gashing a continu- -ous thread the perpendicnlars of which valong a generatrix of the pitch surface-of the hob in development intersect in a point.

19. A hob formed by gashinga continuvous vthread perpendiculars to which along a generatrix of' the pitch surface of the hob in development intersect in va. point Whichlies in a lin-e at right angles to the hob axis. 20, The hob'formedby gashing a continuous thread thev .perpendiculars' to which along a generatrix of the pitch .surface'of the hob in development intersect in a point 21. A taper hob having teeth the normals to which at the pitch surface in development along any radial line intersectin a Vsingle point which is at a distance from the apex of the hob equal to the polar sub-normal thereof. f

22. A taper hob formed by gashing a thread which in` development intersects al .straight line at increasingly. acute angles. l 23. A taper hob formed by gashing al contlnuous thread of constant pitch along a l straight line generatrix of its pitch-surface.v

24. A ,taper hob formed by gashi-nga cons.'

tinuous thread which in axial sectiolfrforms a rack of constant pitch."

25. A taper hob adapted to meshi'with ya-'jbasic crown gear Whose .teeth in al section offsetI from its center form 'a rack stant pitch.

26. A hob formed by gashing a thread general'involute type. j

27. 'A hob formed by gashing a thread of -Which in development forms aspiral ofthe constant pitch which in development forms a spiral of the general Iinvolute type.

28.' A taper hob formed by gashing a l thread vwhich in development forms an Archimedeanspiral. 29. A= taper hob .formed by. gashinga thread `Which in development forms a. spiral 30. A hobfcomprising 'a frus'td'sconical body'provided .with a continuous l'i'.hrcad,-

which in developmentforrnsa spiral of the general involute type, said thread being capable of meshing with' a-rack elementY of`v constant pitch along a straight line generatrix-of pitch surface of hob, said thread beedges.

'inggashed and 'relieved to forxn cutting T `NIKOLA` TRBoJvIcH. 

